The TSP’s New Roth In-Plan Conversion: How to Move Pre-Tax Money to Roth and Lock in a Low Tax Bill

If you’ve got money sitting in the traditional side of your TSP, the government just handed you a new tool to turn it into tax-free Roth money — without taking it out of the plan.

As of January 28, 2026, the TSP lets you do a Roth in-plan conversion: move part of your traditional (pre-tax) balance into a Roth (after-tax) balance, right inside your account. You pay ordinary income tax on whatever you convert this year. After that, it grows tax-free, and qualified withdrawals in retirement come out tax-free.

The catch — and the whole game — is when you do it. Convert in a year your tax rate is rock-bottom, and you pay pennies on the dollar to lock in decades of tax-free growth. Convert in a high-income year, and you’re just handing the IRS money early. For service members, that low-tax year often has a name: deployment.

What a Roth in-plan conversion actually does

Picture two buckets inside your TSP. The traditional bucket is pre-tax — you got a tax break when the money went in, and you’ll owe income tax when you pull it out in retirement. The Roth bucket is the reverse — you already paid tax, so it grows and comes out tax-free.

A Roth in-plan conversion pours money from the traditional bucket into the Roth bucket. The IRS treats the converted amount as taxable income for the year you do it. If you don’t have a Roth balance yet, your first conversion creates one.

This is not a contribution and it’s not a rollover. The TSP confirms a conversion doesn’t touch your contribution elections or your annual contribution limits — those keep running on their own. You’re only moving money you’ve already saved from one tax treatment to another.

Why deployment (or any junior year) is the sweet spot

Here’s the tax logic, plain.

You pay income tax on a conversion at your marginal rate — the rate on your top dollar of income. So the lower your taxable income in the year you convert, the cheaper the conversion.

Two situations push your rate down hard:

• You’re junior enlisted. An E-3 or E-4 is in one of the lowest brackets they’ll ever see. Converting now, while your rate is low, beats converting later as a senior NCO or officer with a bigger paycheck.
• You’re deployed to a combat zone. Under the Combat Zone Tax Exclusion (CZTE), the pay you earn in a designated combat zone is excluded from your federal taxable income. Drop most of a year’s pay out of “taxable income,” and your marginal rate can fall through the floor — sometimes to zero. That’s a year where converting traditional money to Roth might cost you almost nothing in tax.

The principle is simple: pay the tax in your cheapest year, not your most expensive one. A conversion is a bet that your tax rate today is lower than it’ll be when you’d otherwise withdraw. For a lot of younger and deployed service members, that bet is close to a sure thing.

One honest caveat: combat-zone pay and the TSP’s tax-exempt balances get complicated fast. If your traditional balance includes tax-exempt contributions from a combat zone, the tax math on converting them is not something to eyeball. That’s a conversation for a tax pro — more on that below.

The rules, straight from the TSP

Before you touch anything, know the guardrails. These are confirmed on tsp.gov:

• You owe the tax this year. The converted amount becomes part of your taxable income for the year. You’ll pay income tax on it at your rate.
• Pay the tax from outside money. You can’t skim the tax out of your TSP. The IRS bill has to come from a separate source — savings, checking, somewhere outside the plan. Convert $10,000 and you’d better have the tax on that $10,000 sitting in your bank account.
• It’s permanent. A conversion can’t be reversed or undone. There’s no take-backs if your income changes or you regret it.
• $500 minimum. You need a total eligible vested balance of at least $500 to request a conversion.
• Leave $500 behind. You have to keep at least $500 in each non-Roth payroll source you’re converting from.
• 26 per year, max. You can request up to 26 conversions per account in a calendar year.
• No W-2 impact. The conversion won’t show up on your W-2, and it’s separate from the SECURE 2.0 catch-up rules. It’s its own transaction.

You make the request in My Account at tsp.gov. The feature is open to both active and separated participants who meet the balance rules.

The trap: you need cash on hand for the tax

The single biggest way people get burned by conversions is forgetting the tax bill comes due outside the plan.

Say you convert $20,000 in a year where that bumps into a 12% marginal rate. That’s roughly $2,400 in federal income tax you owe — and you can’t pay it from the TSP. If you don’t have that cash set aside, you’ve created a tax problem to solve a tax preference.

So the move only makes sense if you can cover the tax comfortably from savings. In a deep CZTE year where your rate is near zero, that bill might be tiny. In a normal year, run the numbers first.

The TSP built a Roth in-plan conversion calculator at tsp.gov to help you estimate the tax hit before you commit. Use it.

How this pairs with the BRS match

If you’re newer to the TSP, get the foundation right before you think about conversions. The order of operations for most junior service members:

1. Contribute 5% to capture the full BRS match — that’s free government money, and skipping it is the most expensive mistake in the system. (We broke this down in The BRS TSP Match Hack.)
2. Default your own contributions to Roth while your rate is low — same low-tax-bracket logic, applied going forward.
3. Then consider converting existing traditional balances — the new in-plan conversion is the tool for money already sitting in the traditional bucket, including the automatic 1% and match, which always land on the traditional side.

Conversions aren’t a substitute for getting the match. They’re a way to clean up pre-tax money you’ve already accumulated, in a year the tax cost is low.

This is a personal-finance decision — get a second set of eyes

A conversion is irreversible and it raises your taxable income. That’s exactly the kind of move worth running past someone before you click. The TSP itself strongly recommends consulting a tax advisor first.

You have a free option built for this: Military OneSource offers no-cost financial counseling to service members and families. Call 800-342-9647 and ask for a financial counselor, or look for a Personal Financial Counselor through your installation’s Military and Family Readiness Center. Bring your numbers — projected income for the year, your traditional balance, and how much cash you could put toward the tax.

A few questions worth asking them:

• Given my income this year, what marginal rate would the conversion be taxed at?
• How much should I convert to stay under the next bracket?
• If I have combat-zone tax-exempt money, how does that change the math?
• Can I realistically cover the tax from savings?

The short version

• The TSP turned on Roth in-plan conversions on January 28, 2026 — move traditional pre-tax money to Roth inside your account.
• You pay ordinary income tax on the converted amount this year, from outside funds. It’s permanent.
• It doesn’t affect your contribution limits or elections — it only touches money you’ve already saved.
• Do it in your lowest-tax year: junior enlisted years, and especially a combat-zone deployment where CZTE drops your rate.
• You need $500 minimum, must leave $500 in each source, and can do up to 26 conversions a year.
• It’s irreversible — talk to a tax pro or a free Military OneSource counselor (800-342-9647) before you convert.

Last verified: June 2026. Roth in-plan conversion feature, rules, tax treatment, and effective date (live January 28, 2026; announced September 5, 2025) confirmed at tsp.gov. Combat Zone Tax Exclusion is set by the IRS and DoD — verify your specific tax situation with a professional. This is not official tax or financial advice. For free, personalized help, contact a Military OneSource financial counselor at 800-342-9647 or a Personal Financial Counselor at your installation. Not an official VA, DoD, or TSP website.